Nathan Chrismas

Mr. Nathan Chrismas is an evolutionary biologist and PhD student at the Bristol Glaciology Centre, part of the University of Bristol’s School of Geographical Sciences. His research focuses on cyanobacteria, key primary producers in the cryosphere. He is interested in the processes that have led to their colonisation of the polar regions, the molecular mechanisms that allow them to survive in such extreme environments and the impact that they have on global biogeochemical cycles. Chrismas is a keen rock climber and hopes to use these skills to better understand the microbiology of remote and inaccessible regions affected by climate change.

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Nathan Chrismas

As an evolutionary biologist, I am particularly fascinated by microbial life that manages to survive in frozen environments. Among the most important groups of organisms found on the Greenland ice sheet are the cyanobacteria. Along with ice algae these are the plants of the ice sheet, performing oxygenic photosynthesis and generating organic carbon helping to link the microbial food web.

While the ice surface tends to be dominated by algae (although some filamentous cyanobacteria can be seen (Yallop et al., 2012)), cryoconite holes are a different matter where a whole host of cyanobacteria can be found. Cryoconite holes are formed by aggregations of ‘rock dust’ reducing local albedo and forming tiny pools of meltwater full of microbial activity. Cryoconite granules are held together by a matrix of filamentous cyanobacteria and the extracellular polysaccharides (EPS) that they exude. Unicellular species are embedded within the cryoconite matrix. I am interested in finding out just what these species of cyanobacteria are, when they evolved to live in the cold, and what kind of adaptations have allowed them to survive and carry out efficient photosynthesis in such extreme conditions.

Another important question involves the relationship that cyanobacteria might have with the dark snow. If excess black carbon were to cause an increase in heterotrophic bacterial consumption of carbon from external sources instead of carbon fixed by the cyanobacteria (like in the cryoconite holes of Svalbard: see Stibal et al., 2008), then the community composition of the microbial ecosystem may be altered. Cyanobacteria may also interact directly with the black carbon by either increasing the amount of time black carbon spends on the ice, masking it with organic material, drawing it into cryoconite holes or even breaking the black carbon down (Hodson, 2014). Whichever way, the cyanobacteria of the Greenland ice sheet have an undeniable influence on the fate of carbon – which both builds life and accelerates melting – on glacier surfaces, and they remain fascinating organisms for helping to understand the evolution of life in the cold.